What's with this Coolant Overflow? Expanding/purging after shut-down?

[DaniBoy]

I know this has been discussed some, but I have a couple concerns. So this spring I drained my coolant. Filled with water, idled to fan coming on, drained the water and refilled with 50/50. Rode a few times all ok. Then one day I backed out of my garage and there was a 50-cent piece sized puddle of coolant on the floor. Checked reservoir and was good. I rode anyway and came home and parked. I checked underneath and checked again the next day. Dry. Rode many times since. Dry. Then earlier this week I rode and when I got home, I saw the equivalent of maybe an ounce or so of coolant that had run about a foot over to my floor drain (I failed to see it when I backed out). Reservoir is well above MIN mark cold. Cap is tight. I’ve ridden a few times since with no leakage. This is all happening up front near the mid rear of the frunk - in line with the reservoir. When I flushed and refilled the system, I had the reservoir filled to the MAX mark cold. It doesn’t seem anything is leaking, as leaks would always leak and not just every several rides apart. I’m surmising that the system is just “puking” out excess fluid via the overflow that it doesn’t need, due to expansion. I know the last time this happened, the fan was running when I shut the key off. Of course, shutting off the key also cuts power to the fan. Am I correct in thinking that no airflow after shutdown would result in a buildup of heat that could result in continued expansion, thus purging out the overflow?